The invention relates generally to refractory compositions. More specifically, the invention relates to refractory compositions suitable for use in the formation of carbon-containing refractory brick or shape and methods of making such brick or shape.
In the past, refractory products have been produced as unformed compositions, such as ramming, casting, or gunning mixes, and as preshaped objects, such as brick and shapes. The standard rectangular brick, measuring 9" long, 41/2" wide, and 21/2 thick, is most often used to build straight walls. Tapered bricks which form self supporting arches, and tapered bricks with undercut slots on the exterior side from which the brick may be hung, may be used to form curved walls and roofs of a furnace. In addition to such bricks, special shapes have been designed such as corner blocks or edge blocks with curved interior faces, skew block, floor tile, muffle wall tile, and grid sections tile. Moreover, blocks of special shapes may be formed with various shapes and sizes of openings in the block for the insertion of burners and the like. Refractory shapes also include runners, gates, sleeves, nozzles, and troughs used to control the flow of molten material.
Brick and shapes have been formed by hand molding, mechanical pressing, or casting in pre-shaped molds, either as water-based slurries or in molten form. Refractory brick and shape have generally been formed from compositions containing a refractory filler with or without a carbonizable binding material. Coal tar pitch has previously been employed as such a binding material and continues to represent one of the most economical binding agents. However, in both brick and shape applications, coal-tar-bonded refractory compositions have been recognized as generating substantial quantities of noxious fumes during firing. These fumes pose air contamination and occupational health hazards and have been recognized as carcinogenic.
Efforts have been made in the past to replace the coal tar binding materials in refractory compositions. For example, U.S. Pat. No. 4,072,531 issued to Funabiki et al. discloses a blast furnace taphole plugging composition including, inter alia, a lignin-modified phenol-formaldehyde condensation product as a replacement for some or all of the tar binding material. In reference to prior art efforts to substitute conventional phenolic resins for the coal tar binder in similar compositions, Funabiki et al. notes that conventional phenolic resins are disadvantageously expensive.
U.S. Pat. No. 4,022,739, issued to Bove also discloses a binder for taphole plugging compositions which does not generate noxious fumes to the degree experienced with coal tar. The binder of Bove comprises a mixture of a high boiling hydrocarbon derivative and a synthetic resin, which may be a formo-phenolic resin having resorcinol molecules in the polymer chain. In this regard, the use of resorcinol-formaldehyde and phenol-formaldehyde polymers as temporary binders for refractory materials including brick is well known. U.S. Pat. No. 3,007,805, issued to Cline and U.S. Pat. No. 2,938,807, issued to Andersen both disclose the use of phenol-formaldehyde and resorcinol-formaldehyde resins as carbonizable binders for refractory bodies.
Use of phenol-formaldehyde and resorcinol-formaldehyde polymers as the binding material for refractory compositions does not entirely solve the fume problem. More specifically, these polymers commonly contain free formaldehyde. As noted in U.S. Pat. No. 3,917,558 issued to Gardikes et al., the formaldehyde vapors generated during curing are unpleasant, irritating, and pose a health hazard to persons continually exposed to such vapors. Moreover, these polymers may contain 5-10% free phenol, which may also vaporize during curing and thus generate toxic fumes. In addition, fumes from organic solvents employed with some prior art synthetic resin binders were hazardous to manufacturing employees.